Autofocus Modes Explained

Sony recently released a new mirrorless camera that focuses faster than most of the best APS-C sensor equipped cameras on the market. The compact a6000 uses a Hybrid autofocus system which combines both Phase Detection and Contrast Detection autofocus. Now, you probably know that Phase Detection is faster than Contrast Detection, but be honest, do you know why? In this video, the different autofocus modes are explained:

There are two kinds of AF: Phase Detection (found on DSLRs) and Contrast Detection (found on point-and-shoot cameras and smartphones).

Phase Detection Autofocus

Phase Detection has been around for awhile, it is what film SLRs use. The system uses two tiny sensors and an array of lenses to measure the distance between your camera and your subject.

How Phase Detection Works:

The light goes through the lens and hits the mirror behind it

The mirror serves two purposes: it reflects the light up and to the viewfinder so you can see the image; and it is also semi-transparent, with another mirror behind it that reflects the light down to the bottom of the camera where there is a phase detection autofocus sensor

Depending on whether you’re focused in front of or behind the subject, the camera always knows which direction to move the focusing sensor in order to focus

The advantage is really fast focusing

Contrast Detection Autofocus

Contrast Detection is a purely digital system. It uses the camera’s processor to analyze the image and determine at what point, when the focusing lens is moving, that image is at its sharpest, when it has the most contrast.

Advantages and Disadvantages of Contrast Detection

Disadvantages

While it is reliant on the speed of the processor, it also needs to know when it is out of focus from the back direction, as well as the front direction. This means it generally has to overshoot to know that it was in focus beforehand.

It’s not as fast as Phase Detection.

Advantage

The biggest advantage is that it’s very precise because it’s reading the data directly off the sensor. Once that data is in focus it knows the image you capture is going to be directly in focus as well.

Hybrid Autofocus

The Sony a6000 uses Hybrid AF which combines Phase Detection and Contrast Detection. On the sensor, you have lenses which is the Phase Detection part, giving it the ability to focus really quickly on your subject. Then it switches to Contrast Detection to get that nice, crisp quality.

The best parts of each system work together to give you a fast and precise AF. Have you tried out a camera with Hybrid Autofocus?

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